Multi-Satellite Orbit Determination

The practice of tracking the position and velocity state of a spacecraft over time, commonly known as orbit determination, is necessary to successfully operate any orbiting asset. Knowledge of a spacecraft’s state over time is essential to perform core mission functions, execute maneuvers and avoid potential collisions with other objects in space.

In typical single-satellite orbit determination, ground-based tracking measurements are processed to predict a spacecraft’s ephemeris, often as a history of the spacecraft’s position and velocity over time.

Multi-satellite orbit determination involves simultaneously processing measurements of multiple spacecraft within the framework of a single computational estimator. In comparison to the single-satellite case, a multi-satellite estimator is structured to account for the additional satellite states and uncertainties being estimated. In addition, multi-satellite orbit determination allows the estimator to leverage knowledge of the relative motion between satellites. Rather than relying exclusively on ground-based measurements to predict satellite ephemeris, measurements from one satellite to another can be processed by the estimator.

One example is the ability to estimate errors or biases in tracking systems — measurement errors and biases are common to each satellite being tracked and can be more accurately estimated when multiple satellites are considered.

Another particular application that benefits from multi-satellite orbit determination is deploying, operating, and controlling multiple closely-positioned spacecraft, commonly referred to as spacecraft formation flying. Spacecraft formation flying may be desirable for a variety of space mission objectives, including on-orbit vehicle assembly and maintenance, communications and radar applications, successive surface imaging, and many more.

Spacecraft that orbit in close proximity to each other offer a broader range of commercial and scientific functions than is achievable with a single vehicle. The ability to process relative measurements between satellites is beneficial because tight restrictions on relative position and velocity uncertainty are often present in these circumstances.

ODTK is a standalone product that can interface with STK to analyze ephemeris predictions. In addition to providing single-satellite orbit determination capabilities, ODTK facilitates multi-satellite orbit determination where relative measurements between satellites can be considered by the estimator.